use App\Entity\Article;
use App\Form\ArticleType;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Annotation\Route;

...

/**
 * @Route("/articles/create", name="creer_article")
 * @Route("/articles/{id}/edit", name="editer_article")
 */
public function edit(
    Article $article = null,
    Request $request,
    EntityManagerInterface $manager
) {

    // Si l'article est null, on est dans l'ajout d'un nouvel article,
    // sinon on est dans l'édition d'un article existant.
    if(!$article)
        $article = new Article();

    $form = $this->createForm(ArticleType::class, $article);
    $form->handleRequest($request);

    if($form->isSubmitted() && $form->isValid()) {

        // Si c'est un nouvel article, initialiser sa date de création
        if(!$article->getId()) {
            $article->setCreatedAt(new \DateTime());
        }

        $manager->persist($article);
        $manager->flush();

        return $this->redirectToRoute('voir_article', [
            'id' => $article->getId()
        ]);
    }

    return $this->render('articles/edit.html.twig', [
        'formArticle' => $form->createView(),
        'editMode'    => $article->getId() !== null,
    ]);
}